The present invention relates generally to a method and apparatus for detecting the presence of an object. More specifically, the present invention relates to a method and apparatus to distinguish between human and non-human objects, from a movable platform.
Typical intrusion detection systems often consist of one or more types of fixed volumetric detectors. For example, some systems utilize stationary microwave devices that emit microwave radiation at a known frequency and analyze returned radiation to determine changes in frequency induced by moving objects, which produce a Doppler-effect shift in the received radiation. Other systems use passive infrared (IR) detectors sensitive to IR radiation to determine when a heat source, such as a human body, moves into its field of view.
Some systems attempt to reduce the occurrence of false alarms by combining two or more sensors. For instance, a microwave sensor and an IR sensor have been deployed in a vehicle or robot to detect intruders. In such systems, a change in a condition sensed by the first sensor in a target area may cause the second sensor to become aligned with the first sensor. If both sensors indicate a change in respective conditions, an intrusion is indicated. Generally, these systems process each sensor signal separately, and they essentially AND the results together logically to generate an alarm signal.
Each individual sensor signal of such systems is subject to the same drawbacks as single-sensor systems. Single-sensor systems are prone to a relatively high incidence of false alarms because intruders may share similar characteristics with a non-intruder. Further, the use of a passive IR sensor from a moving platform presents at least one additional problem. It is difficult, if not impossible, to determine if a change in average temperature recorded by the IR sensor is due to an intruder or due to a change in the background temperature, because the IR sensor""s field of view changes with its motion.
Traditional intrusion detection systems are not able to provide a simple and low-cost method of performing human detection from a moving platform. Rather, existing intrusion detection techniques often require computationally demanding image processing algorithms. Further, existing systems have not been able to utilize commercial passive infrared or active Doppler sensors to achieve such human detection.
A number of different techniques have been attempted for the detection of a person from a moving platform, but each has been unsuccessful. One method senses motion of the chest during respiration using a small Doppler radar system. However, the signal from such a system may be so small that other disturbances present in the background may overwhelm the signal in question, making its measurement practically impossible. Chemical sensors also have been considered for human presence detection, but their effective detection ranges are on the order of only a few feet. Acoustic sensors have also been considered, but background noise can easily overwhelm the desired signal or cause false alarms. Also, real-time video and infrared cameras with associated image processing have been considered for robotics applications, but the complexity, power consumption, and required computing power are incompatible with a small, battery-powered robot platform.
The present invention addresses shortcomings of the prior art, at least in part, by utilizing differences in the electromagnetic radiation emission and absorption properties of objects, including humans, at two or more separated frequencies to differentiate humans from other objects or from other types of emitters. The present invention may utilize radiation properties of the objects and need not rely on target motion or other characteristics that may be changed easily. The present invention may classify objects that come into the view of one or more moving sensors by contrasting the electromagnetic radiation emission and absorption properties of those objects at different frequencies. For example, a combination of infrared and millimeter wave sensors may be used to identify a desired object, such as a human intruder, even if that object moving. Further, the present invention may be used to identify hot spots within a particular area, such as a forest fire.
The present invention may utilize radiometric sensor data that is analyzed in order to identify characteristics differentiating humans from false targets. The characteristics used to classify an object entering the field may be determined by the properties of the objects themselves. There are several different characteristics that may be used to differentiate a human from some other object. In the present invention, such parameters, some of which may vary depending upon physical characteristics of the object and other possible false targets, may be examined and utilized for determining the presence of an object.
In one aspect, the invention is an apparatus for detecting the presence of an object that includes one or more passive thermal radiation sensors and a calculation circuit. The one or more passive thermal radiation sensors are adapted to detect thermal radiation at two or more differing wavelengths such that emissive and absorption properties of the object are distinguishably different at at least two of the two or more differing wavelengths. The one or more passive thermal radiation sensors generate a plurality of signals responsive to the thermal radiation. The calculation circuit is in operative relationship with the one or more passive thermal radiation sensors and is adapted to compare the plurality of signals to a threshold condition. The calculation circuit outputs an alarm signal when the threshold condition is met, indicating the presence of the object.
In other aspects, the differing wavelengths may differ by about three orders of magnitude. A first wavelength may range from about 1 microns to about 100 microns and another wavelength may range from about 0.1 mm. to about 200 mm. The apparatus may further include a moving platform coupled to the one or more passive thermal radiation sensors. At least two of the one or more passive thermal radiation sensors may include substantially the same field of view. The calculation circuit may include a one-dimensional numerical processing circuit. The object may include a human or a fire. The apparatus may also include a circuit adapted to filter radiometric background signals. The threshold condition may be a predetermined or an adaptively determined threshold condition. The threshold condition may include a ratio of radiometric temperatures of the object. That ratio may be about one. The threshold condition may include a difference in radiometric temperatures of the object. That difference may be greater than about zero. The threshold condition may include an apparent surface area of the object. The apparatus may also include a reflector adapted to direct artificial background radiation towards at least one of the one or more passive thermal radiation sensors.
In another aspect, the invention comprises an apparatus for detecting the presence of an object including an infrared sensor, a millimeter wave sensor, and a calculation circuit. The infrared sensor detects thermal radiation and generates a responsive first signal. The millimeter wave sensor detects thermal radiation and generates a responsive second signal. The calculation circuit is coupled to the infrared sensor and to the millimeter wave sensor. The circuit is adapted to compare the first and second signals with a threshold condition and to output an alarm signal when the threshold condition is met, indicating the presence of the object.
In other aspects, the apparatus may also include a moving platform coupled to the infrared sensor and to the millimeter wave sensor. The apparatus may further include a circuit to filter radiometric background signals. The apparatus may further include a range finding apparatus to determine a range to the object. The apparatus may also include a circuit to determine an apparent surface area of the object. The object may be a human.
In another aspect, the invention comprises a method for determining if an object is an intruder. The method includes detecting thermal radiation from the object at a first wavelength and generating a first responsive signal. It also includes detecting thermal radiation from the object at a second wavelength and generating a second responsive signal. At the first and second wavelengths, the object exhibits distinguishably different emissive and absorption properties. The method also includes comparing the first and second responsive signals to a threshold condition that indicates the object is an intruder.
In other aspects, a passive infrared sensor may detect thermal radiation from the object at the first wavelength and a passive millimeter wave sensor may detect thermal radiation from the object at the second wavelength. The first wavelength may range from about 8 microns to about 14 microns, and the second wavelength may be range from about 0.1 mm. to about 200 mm. The method may also include calculating a first and second apparent radiometric temperature from the first and second responsive signals, respectively. The threshold condition may include a difference between or a ratio of the first and second apparent radiometric temperatures.
In another aspect, the invention comprises a method of monitoring radiometric activity to determine the presence of an object. The method includes receiving a first input signal from a first radiometric sensor adapted to detect a first wavelength, where the first input signal is characteristic of a radiation spectrum of the object at the first wavelength. The method also includes receiving a second input signal from a second radiometric sensor adapted to detect a second wavelength, where the second input signal is characteristic of a radiation spectrum of the object at the second wavelength. The radiation spectrum at the first wavelength is distinguishably different from the radiation spectrum at the second wavelength. The method also includes calculating a first apparent radiometric temperature corresponding to the first input signal and calculating a second apparent radiometric temperature corresponding to the second input signal. The method also includes comparing the first and second apparent radiometric temperatures with a radiometric threshold condition indicative of the presence of the object.
In other aspects, the method may also include determining a range to the object. It may also include determining an apparent surface area of the object. It may further include comparing the apparent surface area to an area threshold condition indicative of the object. The area threshold condition may include an area corresponding to a human. The first radiometric sensor may have a field of view substantially similar to a field of view of the second radiometric sensor. The radiometric threshold condition may include a ratio of said first and second apparent radiometric temperatures, and that ratio may be about 1. The radiometric threshold condition may include a difference between said first and second apparent radiometric temperatures, and that difference may be greater than about zero. The method may also include outputting an alarm signal if the radiometric threshold condition is met. The first sensor may be a passive millimeter wave sensor, and the second sensor may be a passive infrared sensor. The method may also include directing an artificial background radiation towards the first or second radiometric sensors. It may further include distinguishing portions of the first and second input signals corresponding to background from portions of the first and second input signals corresponding to the object. It may also include subtracting the background from the first and second input signals. The steps of receiving the first and second input signals may occur when the first and second radiometric sensors are in motion. The object may be a human.
The present invention, therefore, in one aspect, includes an intrusion detection apparatus, including a plurality of passive thermal radiation sensors adapted to transmit a plurality of sensor signals. At least two of the sensors may be adapted to detect different, and possibly substantially different wavelengths, such that emissive and absorption properties of an intruder differ. A calculation circuit may be employed for receiving, processing, and comparing the processed plurality of sensor signals to a threshold level of an intruder, and for outputting an alarm signal indicating presence of the intruder when the processed plurality of sensor signals exceeds the threshold level, which may be predetermined or adaptively determined.
The present invention may also reside in a target detection apparatus for detecting human presence and object classification including: a first passive radiometric sensor for detecting thermal radiation and generating a first sensor signal and a second passive radiometric sensor for detecting thermal radiation and generating a second sensor signal. The second passive radiometric sensor may be adapted to detect a substantially different wavelength than the first passive radiometric sensor. The apparatus may include a calculation circuit for processing and comparing the processed first and second sensor signals to selected threshold levels for various intruders. In addition, a distance sensor for determining the distance to an object, a thermal radiation sensor, an internally stored map, and a calculation circuit for processing and comparing the radiation signal with the map to predetermined or adaptively determined threshold levels to reduce false alarm rates of intruder detection may be included. Additionally, thermal background radiation may be used to increase range and reduce false alarms (especially in fixed sensor arrangements).